I have a very different response about this.
When everyone is seated for dinner, I would bring up a situation that ‘happened’ recently. I’d say that “I was out for dinner w/friends and one friend brought along another person, someone none of the rest of us knew. Anyway, one of the women (we’ll call her Jane) excused herself to use the restroom, and while she was gone the new person called her a gold-digger. The rest of us were shocked, and we admonished her for the negative comment, and we wondered how she could form such a negative opinion of Jane having only barely known her.” Then look at your nephew’s friend and politely and innocently ask “What do you think would cause someone to say that?!?”
I am certain she would get your message…
Then you can put it to rest.